Morphology of hybrid polystyrene- block-poly(ethylene oxide) micelles: Analytical ultracentrifugation and SANS studies

Morphology and structure of aqueous block copolymer solutions based on polystyrene- block-poly(ethylene oxide) (PS- b-PEO) of two different compositions, a cationic surfactant, cetyl pyridinium chloride (CPC), and either platinic acid (H 2PtCl 6⋅6H 2O) or Pt nanoparticles were studied using a combination of analytical ultracentrifugation (AUC), transmission electron microscopy (TEM), and small angle neutron scattering (SANS). These studies combining methods contributing supplemental and analogous structural information allowed us to comprehensively characterize the complex hybrid systems and to discover an isotope effect when H 2O was replaced with D 2O. In particular, TEM shows formation of both micelles and larger aggregates after incorporation of platinic acid, yet the amount of aggregates depends on the H 2PtCl 6⋅6H 2O concentration. AUC reveals the presence of micelles and micellar clusters in the PS- b-PEO block copolymers solution and even larger (supermicellar) aggregates in hybrids (with CPC). Conversely, SANS applied to D 2O solutions of the similar species indicates that micelles are spherical and no other micellar species are found in block copolymer solutions. To reconcile the SANS and AUC data, we carried out AUC examination of the corresponding D 2O block copolymer solutions. These measurements demonstrate a pronounced isotope effect on micelle aggregation and micelle size, i.e., no micelle aggregation in D 2O solutions, revealing good agreement of AUC and SANS data.